The invention lies in the field of components, in particular microelectronic components and specifically in the field of semiconductor memories.
During the fabrication of components, layers of different materials are successively applied and patterned. In order to ensure the reliability of the fabricated components, the applied layers must have a sufficient adhesion. What is problematic is e.g. the adhesion of insulation materials, e.g. silicon oxide and silicon nitride, on noble metals and other metals that are difficult to oxidize, in particular those from subgroup VIIIb of the periodic table.
Platinum or iridium is used e.g. in the fabrication of the capacitor electrodes of semiconductor memories with a ferroelectric or high-∈-dielectric (∈ generally greater than 20) capacitor dielectric, since this metal is sufficiently resistant to the process conditions required for the deposition of the capacitor dielectric. In particular, the electrodes have to withstand an oxidation at elevated temperatures. However, the pronounced chemical inertness is more of a disadvantage with regard to the adhesion to the standard insulation material used in semiconductor technology. It is presumed that a good adhesion between two layers is connected with a certain chemical interaction or interdiffusion of the adjacent layers. By way of example, a TiAl3 layer forms between titanium and aluminum, and has a favorable effect on the adhesion. Formation of a metal oxide layer in a manner beneficial to adhesion is also observed when depositing metals that are relatively easy to oxidize onto silicon oxide.
In the case of the noble metals or other metals that are difficult to oxidize, there is very little chemical interaction with e.g. oxide layers. Therefore, problems with the adhesion occur particularly frequently in this case. This is critical particularly in the case of increasingly smaller structures, as are found e.g. in semiconductor memories. In that case, the electrodes are formed e.g. by deposition onto a prepatterned insulation layer with subsequent polishing-back (CMP=chemical mechanical polishing). The rotating grinding wheel used for the polishing-back in this case exerts a certain mechanical pressure on the deposited metal layer, which pressure, for lack of adhesion, can lead to a stripping away of the metal layer. Furthermore, cleaning steps after possible etching patterning of the metal layer or during the ultrasonic bonding of finished processed semiconductor chips have also been found to be a particular mechanical burden.
In order to improve the adhesion of noble metals, for example of a storage capacitor of a semiconductor memory, U.S. Pat. No. 5,668,040, teaches providing a layer of a transition metal, e.g. from subgroup IVb, Vb or VIb, between the noble metal of the bottom capacitor electrode and the insulation layer including silicon oxide. This transition metal forms a metal nitride layer at the interface with the noble metal layer during a thermal treatment in an ammonia-containing atmosphere. In this case, the noble metal layer does not react with nitrogen or the transition metal. Furthermore, a metal oxide layer forms at the interface between the transition metal and silicon oxide. What is problematic with this approach, however, is that the etched edges of the transition metal comes into contact with the capacitor dielectric that is subsequently applied, and is oxidized at least there. Moreover, transition metal can diffuse into the capacitor dielectric and impair the dielectric or ferroelectric properties thereof.
In order to avoid the diffusion of a transition metal into the capacitor dielectric, it is possible, as proposed e.g. in Published European Patent Application EP 0 697 718 A1, for the deposition of the capacitor dielectric to be preceded by an oxidation of the edges of the transition metal, in the case of which, however, a considerable increase in volume is observed which can lead to a mechanical fracture of the noble metal layer seated on the transition metal layer. Moreover, the cross section available for the contact connection of the bottom electrode is restricted.
Published German Patent Application DE 198 28 969 A1 describes a method for fabricating a semiconductor component in which a silicon layer is deposited as an adhesion promoter between a top metal electrode of a storage capacitor and an oxide layer.
Issued German Patent DE 196 01 592 C1 discloses, for the purpose of improving the adhesion of a platinum layer on a dielectric carrier layer of a sensor, providing a platinum silicide layer between the dielectric carrier layer and the platinum layer. The platinum silicide layer is fabricated by siliconizing a silicon layer applied before the deposition of the platinum layer.
It is accordingly an object of the invention to provide a method for fabricating a component, which overcomes the above-mentioned disadvantages of the prior art methods of this general type.
In particular, it is an object of the invention to provide a method for fabricating a component with an improved adhesion of a noble metal layer to an insulation layer.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for fabricating a component including steps of: applying a noble metal layer to a substrate and subsequently applying a silicon layer to the substrate such that a surface of the noble metal layer contacts the silicon layer; performing a siliconization such that the surface of the noble metal layer contacting the silicon layer is siliconized; performing an oxidation to oxidize a silicide layer formed from the silicon layer; and applying an insulation layer.
In accordance with an added feature of the invention, when performing the oxidation step, unsiliconized regions of the silicon layer that may have remained are oxidized.
In accordance with an additional feature of the invention, the siliconization step is effected in situ while performing the step of applying the silicon layer.
In accordance with another feature of the invention, the method includes patterning the noble metal layer before performing the step of applying the silicon layer.
In accordance with a further feature of the invention, the method includes: performing the step of applying the noble metal layer by applying the noble metal layer to a ferroelectric or dielectric capacitor dielectric covering a further noble metal layer; forming a stack by patterning the further noble metal layer, the capacitor dielectric, and the noble metal layer using a common mask; and conformally depositing the silicon layer onto the stack, and siliconizing and oxidizing the silicon layer such that the silicon layer is completely oxidized in a region directly contacting the capacitor dielectric.
In accordance with a further added feature of the invention, the step of applying the insulation layer is performed after the step of performing the oxidation.
In accordance with a further additional feature of the invention, the method includes: before performing the oxidation, patterning the noble metal layer and the silicon layer by using a lithographically fabricated mask.
In accordance with yet an added feature of the invention, the method includes: introducing at least one contact hole into the insulation layer and into the oxidized silicide layer; and filing the contact hole with a conductive material producing an electrically conductive connection to the noble metal layer.
In accordance with yet an additional feature of the invention, the method includes: after forming the contact hole, removing silicide located at a bottom of the contact hole.
In accordance with yet another feature of the invention, the method includes: fabricating a semiconductor memory having a plurality of storage capacitors, each one of the plurality of storage capacitors having two electrodes and a capacitor dielectric lying between the two electrodes, at least one of the two electrodes being formed by the noble metal layer.
With the foregoing and other objects in view there is also provided, in accordance with the invention, a method for fabricating a component, which includes steps of: applying an insulation layer to a substrate, subsequently applying a silicon layer to the substrate, and subsequently applying a noble metal layer to the substrate such that a surface of the noble metal layer contacts the silicon layer; performing a siliconization such that the surface of the noble metal layer contacting the silicon layer is siliconized; and performing an oxidation to oxidize a silicide layer formed from the silicon layer.
In accordance with an added feature of the invention, when performing the oxidation step, unsiliconized regions of the silicon layer that may have remained are oxidized.
In accordance with an additional feature of the invention, the method includes: performing the siliconization step and the oxidation step during a common thermal treatment in an oxygen-containing atmosphere.
In accordance with another feature of the invention, the thermal treatment is performed in a presence of water vapor.
In accordance with a further feature of the invention, in the oxidation step, the silicide layer and unsiliconized regions of the silicon layer that may have remained are completely oxidized.
In accordance with a further added feature of the invention, the method includes: coordinating a thicknesses of the silicon layer and a thickness of the noble metal layer with one another such that, in an event of a complete siliconization of the silicon layer, the noble metal layer is only partially consumed and a surface of the noble metal layer that is remote from the silicon layer remains essentially free of suicides.
In accordance with a further additional feature of the invention, the step of applying the noble metal layer includes applying the noble metal layer with a thickness 10 to 20 times greater than a thickness of the silicon layer.
With the foregoing and other objects in view there is also provided, in accordance with the invention, a method for fabricating a component, which includes steps of: applying a noble metal layer to a substrate; at an elevated temperature, exposing the noble metal layer to an atmosphere including at least one silane so that a silicide layer is formed at a surface of the noble metal layer; and applying an insulation layer.
In accordance with an added feature of the invention, the silane is an unsubstituted silane.
In accordance with an additional feature of the invention, the silane is a carbon-free silane. In accordance with another feature of the invention, the silane is SinH2n+2, where nxe2x89xa71.
In accordance with a further feature of the invention, the elevated temperature is above 300xc2x0 C.
In accordance with a further added feature of the invention, the elevated temperature is above 600xc2x0 C.
In accordance with a further additional feature of the invention, the noble metal layer is a metal selected from a group consisting of ruthenium, rhodium, palladium, rhenium, osmium, platinum, iridium, and gold.
With the foregoing and other objects in view there is also provided, in accordance with the invention, a component including: a noble metal layer made of a material and having a surface; an insulation layer; and a mixed layer serving as an adhesion promoting layer. The surface of the noble metal layer faces the insulation layer. The mixed layer is formed at the surface of the noble metal layer. The mixed layer includes silicon, oxygen, and the material of the noble metal layer.
With the foregoing and other objects in view there is also provided, in accordance with the invention, a semiconductor memory that includes: a plurality of storage capacitors each having two electrodes; a noble metal layer made of a material and having a surface; an insulation layer, and a mixed layer serving as an adhesion promoting layer. The surface of the noble metal layer faces the insulation layer. The mixed layer is formed at the surface of the noble metal layer. The mixed layer includes silicon, oxygen, and the material of the noble metal layer. At least one of the two electrodes is formed by the noble metal layer.
In other words, the object of the invention can be achieved by a method for fabricating a component having the following steps:
a noble metal layer and a silicon layer, which comes into contact with a surface of the noble metal layer, are applied in this order to a substrate;
a siliconization is carried out, in which the surface of the noble metal layer which is in contact with the silicon layer is siliconized;
an oxidation is carried out, in which the silicide layer formed and unsiliconized regions of the silicon layer that may have remained are oxidized; and
an insulation layer is applied.
Through the siliconization and oxidation, the applied silicon layer is converted into an oxidized silicide layer. This makes use of the insight that noble metals can be siliconized comparatively simply. The adhesion between the noble metal layer and the silicide layer is very good. The silicide layer formed can subsequently be oxidized in order to provide a good adhesion support for an insulation layer. The siliconization and the oxidation result in a layer with comparatively high intermixing or interdiffusion of silicide or noble metal and silicon oxide. As a result, a relatively large inner surface is formed between the silicide or the noble metal and the silicon oxide, the surface contributing to the improved adhesion. Expressed in a simplified manner, it could also be said that a multilayer adhesion layer is formed which has, proceeding from the noble metal layer, a silicide layer, a mixed layer essentially including noble metal and silicon oxide and a silicon oxide layer. With a silicon layer applied comparatively thin, essentially only a mixed layer is discernible, the concentration of the silicide increasing toward the noble metal layer and that of silicon oxide increasing toward the insulation layer. Generally, it is also possible to speak of a superficial silicon oxide layer on a silicide layer. The precise way in which the oxidized silicide layer is constructed depends to a great extent on the layer thickness of the applied silicon layer, the temperature and the time duration of the siliconization and the oxidation.
The interdiffusion of silicide and silicon oxide is a consequence of the siliconization and oxidation, so that it is also possible to speak of reactive intermixing, i.e. an intermixing on account of different chemical reactions. What has a beneficial effect in this case is that the oxidation begins on the side remote from the noble metal surface, but the siliconization begins on the side of the silicon layer which faces the noble metal layer. Therefore, the two reactions run spatially toward one another.
The oxidation of silicides is described e.g. in S. P. Murarka, xe2x80x9cSilicides for VLSI Applicationsxe2x80x9d, Academic Press, 1983, 102-143. It can be assumed in a simplified manner that silicide formed in the case of noble metals decomposes and silicon oxide arises. Further indications with regard to the mechanisms executed can be gathered from the technical article by S. Mantl, xe2x80x9cSilicid-Mikrostrukturen durch lokale Oxidationxe2x80x9d [xe2x80x9cSilicide microstructures through local oxidationxe2x80x9d], Physikalische Blxc3xa4tter 51 (1995), 951-953. Detailed investigations with regard to the siliconization of noble metal layers, in particular of platinum, are described in C. Canali et al., xe2x80x9cPt2Si and PtSi formation with high-purity PT thin filmsxe2x80x9d, Applied Physics Letters, Vol. 31, No. 1, 1977, 43-45.
A further advantage of the method resides in the use of materials that are usually used in the fabrication of components, in particular semiconductor components. Silicon, silicides and silicon oxide are standard materials that are readily controlled technologically.
The siliconization and the oxidation are preferably effected during a common thermal treatment in an oxygen-containing atmosphere. The thermal loading on remaining structures is reduced by virtue of the common treatment. Moreover, oxidized silicide layers fabricated in this way impart a particularly good adhesion between the noble metal layer and the insulation layer. In the case of fabricating semiconductor memories with ferroelectric (e.g. SBT=Strontium Bismuth Tantalate or PZT=lead zirconium titanate) or high-∈ dielectric (BST=Barium Strontium Titanate), the thermal treatment can also be effected in the context of the oxidative treatment of the dielectric.
The siliconization and oxidation can also be carried out in separate steps. Irrespective of the method progression, the surface of the noble metal layer, which is remote from the silicon layer remains free of oxides or silicides.
Without wishing to be restrictive, the mechanism underlying the formation of the oxidized silicon layer is understood as follows in the case of the thermal treatment in an oxygen-containing atmosphere. During the thermal treatment, which is performed at a sufficiently high temperature for the siliconization, the side of the silicon layer which faces the noble metal layer is converted into a silicide layer, while the surface of the silicon layer which is remote from the noble metal layer is oxidized. Accordingly, a silicide layer covered by a silicon oxide layer is initially formed. As the thermal treatment progresses, the silicide decomposes to an increasing extent. The liberated silicon diffuses in the direction of the oxidative atmosphere, that is to say in the direction of the silicon oxide layer already formed. What is thereby achieved at the same time is that no silicon can diffuse through the noble metal to the opposite surface. This surface remains free of silicide in this case. Finally, as the oxidation continues, the initially formed silicide is converted almost completely into silicon oxide and metal, the intermixing being preserved for improvement of the adhesion. The sequence outlined above also corresponds, in principle, to that in the case of separate siliconization and oxidation. Even with initially complete siliconization, silicon oxide forms at the expense of the silicide during the subsequent oxidation. A silicon oxide layer that is greatly intermixed with the noble metal is produced as a result. The extent to which silicide remains depends, in particular, on the temperature and the duration of the treatment.
Particularly preferably, the thermal treatment is effected in the presence of water vapor in order to further reduce the thermal loading, since the oxidation of silicides advances more rapidly in the case of an atmosphere containing water vapor. Alternative methods for the siliconization and the oxidation such as e.g. laser annealing and e-beam scanning are likewise possible.
Preferably, the silicon layer is converted in its entirety in order to achieve the best possible adhesion.
Furthermore, it is preferred if the thicknesses of the silicon layer and of the noble metal layer are coordinated with one another in such a way that, in the event of a complete siliconization of the silicon layer, the noble metal layer is only partially consumed and the surface of the noble metal layer which is remote from the silicon layer remains essentially free of silicides. In this case, the silicon layer should preferably be significantly thinner than the noble metal layer. By way of example, a noble metal layer which is about 10 to 20 times as thick is favorable.
The silicon layer is preferably deposited as a polycrystalline or amorphous layer. Methods suitable for this are e.g. sputtering or plasma-enhanced CVD methods. It is furthermore favorable if silicide is formed in situ during the deposition of the silicon layer. The conditions necessary for this, in particular the required temperature, can easily be realized.
Preferably, the noble metal layer is patterned before the application of the silicon layer, so that edges and side regions of the noble metal layer are also covered by the silicon layer.
It is favorable if:
the noble metal layer is applied to a ferroelectric or dielectric capacitor dielectric covering a further noble metal layer;
the further noble metal layer, the capacitor dielectric and the noble metal layer are patterned using a common mask to form a stack; and
the silicon layer is deposited conformally onto the stack, siliconized and oxidized, the silicon layer being completely oxidized in the region of direct contact with the capacitor dielectric.
The silicon layer should cover the stack as completely as possible. In the region of the capacitor dielectric, the silicon layer is not siliconized, but rather only completely oxidized, so that, peripherally at the outer side of the stack, a completely insulating region is formed within the silicon layer. The noble metal layer and the further noble metal layer are thus electrically insulated from one another.
The application of the insulation layer after the oxidation is likewise preferred, in order to enable an oxidation that is as undisturbed and as complete as possible. If the insulation layer includes silicon oxide, it can also be applied before the oxidation, since silicon oxide is permeable to oxygen. In the case of silicon nitride as an insulation layer, it should be taken into consideration that silicon nitride is an oxygen barrier, so that a correspondingly long time duration must be provided in the case of a subsequent oxidation, depending on the thickness of the silicon nitride layer.
It is furthermore favorable if, before the oxidation, the noble metal layer and the silicon layer are patterned using a mask which is fabricated lithographically. In this case, it is advantageously possible to utilize the properties of the silicon layer as an antireflection layer (ARC=antireflective coating). The deposition of the silicon layer by sputtering is particularly preferable in this case.
It has furthermore been found to be preferred for at least one contact hole to be introduced into the insulation layer and into the oxidized silicide layer and to be filled with a conductive material which produces an electrically conductive connection to the noble metal layer. In this case, after the formation of the contact hole, silicide present at the bottom of the contact hole may be removed in order to reduce the electrical contact resistance. The removal of residual silicide is recommended particularly in the case of iridium as material of the noble metal layer since otherwise the contact resistance is very high.
The material of the noble metal layer is preferably a metal from the group ruthenium, rhodium, palladium, rhenium, osmium, platinum, iridium and gold. Platinum and iridium are particularly preferred. Alloys of the noble metals mentioned are also possible.
The invention is furthermore achieved by a method for fabricating a component having the following steps:
an insulation layer, a silicon layer and a noble metal layer, which comes into contact with the silicon layer, are applied in this order to a substrate;
a siliconization is carried out, in which that surface of the noble metal layer which is in contact with the silicon layer is siliconized; and
an oxidation is carried out in which the silicide layer formed and unsiliconized regions of the silicon layer that may have remained are oxidized.
In this case, the noble metal layer with an underlying silicon layer is applied to the insulation layer. The siliconization and the oxidation likewise lead here to the oxidized silicide layer described further above. The siliconization and oxidation can likewise be carried out in a common thermal treatment.
The invention is furthermore achieved by a method for fabricating a component having the following steps:
a noble metal layer is applied to a substrate;
the noble metal layer is exposed, at elevated temperature, to an atmosphere containing at least one silane, so that a silicide layer is formed at the surface of the noble metal layer; and
an insulation layer is applied.
In this case, the temperatures should be chosen to be high enough that the silane undergoes thermal decomposition. The requisite temperatures of about 300 to 700xc2x0 C. lie above that required for the siliconization, so that a silicide layer forms in situ on the noble metal surface. By contrast, the deposited silicon is not converted on regions of the insulation layer or of the substrate which are not covered by the noble metal layer. Optionally, an oxidation may subsequently be carried out in order further to improve the adhesion. Without oxidation, the adhesion to the insulation layer that is finally applied is promoted just by the silicide layer formed in situ, which is sufficient for many purposes.
Silanes of the general formula SinHxRy where nxe2x89xa71 and x, yxe2x89xa70 are employed. In this case, Ry denotes a radical, which is e.g. CH3, NH2, halogens, in particular F or C.
An unsubstituted silane, in particular a carbon-free silane, is preferably used. Carbon-free silanes have the advantage, in particular, of producing carbon-free silicides, or of preventing the incorporation of carbon into the SiO2/noble metal mixed phase.
Silanes of the form SinH2n+2 where n greater than 1, in particular silane SiH4), disilane (Si2H6) and trisilane (Si3H8), are particularly preferred.
During the deposition, the elevated temperature should lie above 300xc2x0 C., in particular above 600xc2x0 C.
The method is preferably used for fabricating a semiconductor memory having a multiplicity of storage capacitors each having two electrodes and a capacitor dielectric lying in between, at least one of the two electrodes being formed by the noble metal layer.
The invention furthermore relates to a component having a noble metal layer and an insulation layer. Such a component is known from Issued German Patent DE 196 01 592 C1 already cited.
In order to improve the adhesion between the noble metal layer and the insulation layer, the invention proposes that a mixed layer serving as an adhesion promoting layer is formed at the surface of the noble metal layer which faces the insulation layer. The mixed layer includes the material of the noble metal layer, silicon and oxygen.
The mixed layer can be obtained in particular by using the inventive method. The material of the noble metal layer is in particular a metal from the group ruthenium, rhodium, palladium, rhenium, osmium, platinum, iridium and gold. Platinum and iridium are particularly preferred. Alloys of the noble metals mentioned are also possible. Preferably, a ferroelectric or dielectric capacitor dielectric adjoins the surface of the noble metal layer which is remote from the insulation layer.
Preferably, the component is a semiconductor memory having a multiplicity of storage capacitors, at least one of the two electrodes being formed by the noble metal layer.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for fabricating a component, and component having a metal layer and an insulation layer, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.